1. Field
The present invention relates generally to wireless communication, and particularly to reverse link rate allocation for packet data transmissions.
2. Background
In a wireless communication system, such as a system supporting packetized data communications, a radio link for transmissions from an Access Network (AN), or system infrastructure, to an Access Terminal, or remote user, is referred to as a downlink or Forward Link (FL). The radio link for transmissions from the AT to the AN is referred to as the uplink or Reverse Link (RL). Each AT determines an appropriate data rate for RL transmissions. Various methods for determining RL transmission rates from an AT are discussed in “SYSTEM AND METHOD FOR PERSISTENCE-VECTOR-BASED MODIFICATION OF USAGE RATES,” by Rajesh Pankaj, et al., having U.S. patent application Ser. No. 09/410,199, filed on Sep. 30, 1999, and assigned to the assignee hereof.
In a High Data Rate system, such as a system supporting the “cdma2000 High Rate Packet Data Air Interface Specification,” referred to herein as “1xEV-DO,” or IS-856, the AT autonomously determines a data rate for transmissions on the RL based on a probabilistic algorithm that considers the amount of data pending, the available transmit power or PA (power amplifier) headroom, the closed loop resource allocation calculation, and the maximum data rate as indicated to the AT by the AN. The AN assigns probabilities to each of the possible rate transitions that an AT may make. Each AT uses the same probabilities, which are predetermined and set at each AT.
Additionally, each AT implements a power control mechanism to adjust the transmit power dynamically. The adjust in AT transmit power compensates for changes in AT location, shadowing and fading experienced by the AT and the transmit data rate. As an AT moves farther away from a Base Station (BS) in the Active Set (AS) of the AT, the transmit power of the AT increases to compensate. Generally, as an AT moves toward a sector boundary, the interference caused by the AT in question to other AT's is increased due to an increase in the AT transmit power.
As the rate allocation algorithm considers the transmit power, an AT far from the AN, or otherwise experiencing a poor channel condition, relative to other ATs, may be subject to low data rates for an extended time period. In many communication systems, however, there is a desire to provide an equal grade of service. In other words, each AT is provided an approximately equal opportunity to transmit data on the RL without regard to channel condition so as not to penalize an AT for moving within the system. However, this mechanism does not take into account the interference due to an AT.
An increase in data rate results in an increase in the interference caused by an AT to other ATs in the system and therefore, there is a desire to discourage and/or prohibit that AT from transmitting at higher rates if that AT is likely to cause excessive interference to other AT's in the system. Further, there is a desire for each AT to transmit at maximum rate conditioned on equal interference considering all ATs in the system.
There is a need, therefore, for AT rate allocation that balances an equal grade of service goal with the desire to maximize capacity of the system. Similarly, there is a need for AT rate allocation that provides a robust RL and reduces interference to other users. There is further a need for reverse link rate allocation to achieve better control over other-cell interference and improve system stability.